The present invention relates to a taking optical system, and, particularly, to a taking optical system which can cope with different frame-formats (i.e. different numbers of pixels), for example a taking optical system that can be used with image sensing devices having different frame-formats.
In recent years, as personal computers become prevalent, digital still cameras have been coming into wider and wider use that allow easy storage of images as electronic data. Such digital still cameras employ an image sensing device. In the modern design of image sensing devices, there are two mutually conflicting trends: one toward smaller frame-formats in keeping with the demand for more compact and more inexpensive cameras, and the other toward higher resolutions within given frame-formats in keeping with the demand for higher quality in images obtained.
For this reason, in the modern design of digital still cameras, it is customary to use, in combination with image sensing devices having different frame-formats according to their respective applications, taking optical systems dedicated exclusively thereto. Thus, developing a taking optical system that can be used with image sensing devices having different frame-formats is expected to lead to a considerable reduction in the costs of taking optical systems in general that are designed for similar applications.
As one example of a taking optical system that can be used with image sensing devices having different frame-formats, it has conventionally been known to apply simply a taking optical system designed for a relatively large frame-format to a relatively small frame-format. As another example, Japanese Laid-Open Patent Applications Nos. H8-114742 and H10-319314 propose using a relay lens system which refocuses the images formed by a taking optical system so as to vary the magnification. As another example, Japanese Laid-Open Patent Applications Nos. H10-123416, H9-329743, H9-329744, and H7-199067 propose disposing a detachable or exchangeable conversion lens unit somewhere in the optical path of a taking optical system so that the construction of the taking optical system can be changed in accordance with the frame-format by detaching or exchanging the conversion lens unit.
However, the first conventional method mentioned above of applying a taking optical system designed for a large frame-format to a small frame-format is impractical, not only because the taking optical system is unduly large relative to a small frame-format, but also because, due to the relationship between the angle of view and the focal length, the focal-length range is shifted toward the longest-focal-length side. The second conventional method mentioned above of using a relay lens system requires securing an extra optical path for the relay lens system, and thus makes the taking optical systems as a whole extremely large.
The third conventional method mentioned above of changing the construction of a taking optical system in accordance with the frame-format by detaching or exchanging a conversion lens unit provided therein requires that the structures of the individual lens barrels for holding the constituent lens units of the taking optical system be changed in accordance with the frame-format, or that the middle portion of the taking optical system be made movable so as to allow the conversion lens unit to be detached or exchanged, and thus makes the design of the taking optical system extremely complicated.
An object of the present invention is to provide a taking optical system that can be used with image sensing devices having different frame-formats and that offers satisfactorily high image quality despite being compact.
To achieve the above object, according to one aspect of the present invention, a method of converting a frame-format in a taking optical system comprises steps of arranging a plurality of lens units constituting the taking optical system except for the lens unit disposed at the object-side end or at the image-side end and determining the configuration of the lens unit disposed at the object-side end or at the image-side end based on the desired frame-format.
According to another aspect of the present invention, a taking optical system is composed of a main optical system that can form an object image on its own and a conversion optical system that can be removably disposed at the image-side end of the main optical system, wherein, when the object image is taken as the image of the first frame-format, the main optical system alone is used, and, when the object image is taken as the image of the second frame-format that is different from the first frame-format, the main optical system is used with the conversion optical system disposed at the image-side end thereof.
According to another aspect of the present invention, an image taking apparatus is provided with a taking optical system. The taking optical system is composed of a main optical system that can form an object image on its own and a conversion optical system that can be removably disposed at the image-side end of the main optical system, wherein, when the object image is taken as the image of the first frame-format, the main optical system alone is used, and, when the object image is taken as the image of the second frame-format that is different from the first frame-format, the main optical system is used with the conversion optical system disposed at the image-side end thereof. The image taking apparatus can cope with both of the first and second frame-formats.
According to another aspect of the present invention, a method of converting a frame-format in a taking optical system comprises a step of designing the taking optical system to have a main optical system that can form an object image on its own and a conversion optical system that can be removably disposed at the image-side end of the main optical system, and a step of using the main optical system alone when the object image is taken as the image of the first frame-format and using the main optical system with the conversion optical system disposed at the image-side end thereof when the object image is taken as the image of the second frame-format that is different from the first frame-format.
According to another aspect of the present invention, a taking optical system is provided with, from the object side, an object-side lens unit and a plurality of lens units disposed behind the object-side lens unit and performs zooming by moving, of the object-side lens unit and the lens units disposed behind it, at least two lens units along the optical axis, wherein, when an object image is taken as the image of the first frame-format, as the object-side lens unit, a first object-side lens unit is used, and, when the object image is taken as the image of the second frame-format that is larger than the first frame-format, as the object-side lens unit, a second object-side lens unit is used that is differently configured from the first object-side lens unit, and wherein the following condition is fulfilled:
0.65 less than f1b/f1s less than 0.95
wherein
f1s represents the focal length of the first object-side lens unit; and
f1b represents the focal length of the second object-side lens unit.
According to another aspect of the present invention, a taking optical system is provided with, from the object side, an object-side lens unit and a plurality of lens units disposed behind the object-side lens unit and performs zooming by moving, of the object-side lens unit and the lens units disposed behind it, at least two lens units along the optical axis, wherein, when an object image is taken as the image of the first frame-format, as the object-side lens unit, a first object-side lens unit is used, and, when the object image is taken as the image of the second frame-format that is different from the first frame-format, in the zoom range between the middle-focal-length position and the telephoto end of the taking optical system as determined using the first object-side lens unit, as the object-side lens unit, a second object-side lens unit is used that is differently configured from the first object-side lens unit.
According to another aspect of the present invention, a taking optical system is provided with, from the object side, a positively-powered object-side lens unit, a negatively-powered second lens unit, and lens units disposed behind them and performs zooming by moving, of these lens units, at least two lens units along the optical axis, wherein, when an object image is taken as the image of the first frame-format, as the object-side lens unit, a first object-side lens unit is used, and, when the object image is taken as the image of the second frame-format that is larger than the first frame-format, as the object-side lens unit, a second object-side lens is used that is differently configured from the first object-side lens unit.
According to another aspect of the present invention, an image taking apparatus is provided with a taking optical system. The taking optical system is provided with, from the object side, an object-side lens unit and a plurality of lens units disposed behind the object-side lens unit and performs zooming by moving, of the object-side lens unit and the lens units disposed behind it, at least two lens units along the optical axis, wherein, when an object image is taken as the image of the first frame-format, as the object-side lens unit, a first object-side lens unit is used, and, when the object image is taken as the image of the second frame-format that is larger than the first frame-format, as the object-side lens unit, a second object-side lens unit is used that is differently configured from the first object-side lens unit, and wherein the condition noted above is fulfilled. The image taking apparatus can cope with both of the first and second frame-formats.
According to another aspect of the present invention, a method of converting a frame-format in a taking optical system comprises a step of designing the taking optical system to have, from the object side, an object-side lens unit and a plurality of lens units disposed behind it and to perform zooming by moving, of the object-side lens unit and the lens units disposed behind it, at least two lens units along the optical axis and a step of using, as the object-side lens unit, a first object-side lens unit when an object image is taken as the image of the first frame-format and using, as the object-side lens unit, a second object-side lens unit that is differently configured from the first object-side lens unit when the object image is taken as the image of the second frame-format that is larger than the first frame-format, wherein the following condition is fulfilled:
0.65 less than f1b/f1s less than 0.95
wherein
f1s represents the focal length of the first object-side lens unit; and
f1b represents the focal length of the second object-side lens unit.
According to another aspect of the present invention, a method of converting a frame-format in a taking optical system comprises a step of designing the taking optical system to have, from the object side, an object-side lens unit and a plurality of lens units disposed behind it and to perform zooming by moving, of the object-side lens unit and the lens units disposed behind it, at least two lens units along the optical axis and a step of using, as the object-side lens unit, a first object-side lens unit when an object image is taken as the image of the first frame-format and using, as the object-side lens unit, a second object-side lens unit that is differently configured from the first object-side lens unit when the object image is taken as the image of the second frame-format that is different from the first frame-format in the zoom range between the middle-focal-length position and the telephoto end of the taking optical system as determined using the first object-side lens unit.
According to still another aspect of the present invention, a method of converting a frame-format in a taking optical system comprises a step of designing the taking optical system to have, from the object side, a positively-powered object-side lens unit, a negatively-powered second lens unit, and lens units disposed behind them and to perform zooming by moving, of these lens units, at least two lens units along the optical axis and a step of using, as the object-side lens unit, a first object-side lens unit when an object image is taken as the image of the first frame-format and using, as the object-side lens unit, a second object-side lens unit that is differently configured from the first object-side lens unit when the object image is taken as the image of the second frame-format that is larger than the first frame-format.